[Xen-devel] [PATCH 3/4] x86/vvmx: correctly emulate VMWRITE

[Sergey Dyasli <sergey.dyasli@xxxxxxxxxx>]

There is an issue with the original __vmwrite() in nested vmx mode:
emulation of a guest's VMWRITE with invalid arguments leads to BUG().

Fix this by using __vmwrite_safe() and reporting any kind of VMfail
back to the guest.

Signed-off-by: Sergey Dyasli <sergey.dyasli@xxxxxxxxxx>
---
 xen/arch/x86/hvm/vmx/vmcs.c        |  9 +++++++--
 xen/arch/x86/hvm/vmx/vvmx.c        | 15 +++++++++++----
 xen/include/asm-x86/hvm/vmx/vmcs.h |  2 +-
 xen/include/asm-x86/hvm/vmx/vvmx.h |  4 ++--
 4 files changed, 21 insertions(+), 9 deletions(-)

diff --git a/xen/arch/x86/hvm/vmx/vmcs.c b/xen/arch/x86/hvm/vmx/vmcs.c
index 641e2ef..c1f09c6 100644
--- a/xen/arch/x86/hvm/vmx/vmcs.c
+++ b/xen/arch/x86/hvm/vmx/vmcs.c
@@ -943,11 +943,16 @@ u64 virtual_vmcs_vmread(const struct vcpu *v, u32 
vmcs_encoding)
     return res;
 }
 
-void virtual_vmcs_vmwrite(const struct vcpu *v, u32 vmcs_encoding, u64 val)
+unsigned long virtual_vmcs_vmwrite(const struct vcpu *v, u32 vmcs_encoding,
+                                   u64 val)
 {
+    unsigned long ret;
+
     virtual_vmcs_enter(v);
-    __vmwrite(vmcs_encoding, val);
+    ret = __vmwrite_safe(vmcs_encoding, val);
     virtual_vmcs_exit(v);
+
+    return ret;
 }
 
 /*
diff --git a/xen/arch/x86/hvm/vmx/vvmx.c b/xen/arch/x86/hvm/vmx/vvmx.c
index e0cf0fb..c427a24 100644
--- a/xen/arch/x86/hvm/vmx/vvmx.c
+++ b/xen/arch/x86/hvm/vmx/vvmx.c
@@ -264,7 +264,7 @@ u64 get_vvmcs_real(const struct vcpu *v, u32 encoding)
     return virtual_vmcs_vmread(v, encoding);
 }
 
-void set_vvmcs_virtual(void *vvmcs, u32 vmcs_encoding, u64 val)
+unsigned long set_vvmcs_virtual(void *vvmcs, u32 vmcs_encoding, u64 val)
 {
     union vmcs_encoding enc;
     u64 *content = (u64 *) vvmcs;
@@ -298,11 +298,13 @@ void set_vvmcs_virtual(void *vvmcs, u32 vmcs_encoding, 
u64 val)
     }
 
     content[offset] = res;
+
+    return 0;
 }
 
-void set_vvmcs_real(const struct vcpu *v, u32 encoding, u64 val)
+unsigned long set_vvmcs_real(const struct vcpu *v, u32 encoding, u64 val)
 {
-    virtual_vmcs_vmwrite(v, encoding, val);
+    return virtual_vmcs_vmwrite(v, encoding, val);
 }
 
 static unsigned long reg_read(struct cpu_user_regs *regs,
@@ -1740,13 +1742,18 @@ int nvmx_handle_vmwrite(struct cpu_user_regs *regs)
     unsigned long operand; 
     u64 vmcs_encoding;
     bool_t okay = 1;
+    unsigned long err;
 
     if ( decode_vmx_inst(regs, &decode, &operand, 0)
              != X86EMUL_OKAY )
         return X86EMUL_EXCEPTION;
 
     vmcs_encoding = reg_read(regs, decode.reg2);
-    set_vvmcs(v, vmcs_encoding, operand);
+    if ( (err = set_vvmcs(v, vmcs_encoding, operand)) )
+    {
+        vmfail(regs, err);
+        return X86EMUL_OKAY;
+    }
 
     switch ( vmcs_encoding & ~VMCS_HIGH(0) )
     {
diff --git a/xen/include/asm-x86/hvm/vmx/vmcs.h 
b/xen/include/asm-x86/hvm/vmx/vmcs.h
index cb02d53..b30e0f7 100644
--- a/xen/include/asm-x86/hvm/vmx/vmcs.h
+++ b/xen/include/asm-x86/hvm/vmx/vmcs.h
@@ -541,7 +541,7 @@ int vmx_check_msr_bitmap(unsigned long *msr_bitmap, u32 
msr, int access_type);
 void virtual_vmcs_enter(const struct vcpu *);
 void virtual_vmcs_exit(const struct vcpu *);
 u64 virtual_vmcs_vmread(const struct vcpu *, u32 encoding);
-void virtual_vmcs_vmwrite(const struct vcpu *, u32 encoding, u64 val);
+unsigned long virtual_vmcs_vmwrite(const struct vcpu *, u32 encoding, u64 val);
 
 static inline int vmx_add_guest_msr(u32 msr)
 {
diff --git a/xen/include/asm-x86/hvm/vmx/vvmx.h 
b/xen/include/asm-x86/hvm/vmx/vvmx.h
index 242e524..d60e0bb 100644
--- a/xen/include/asm-x86/hvm/vmx/vvmx.h
+++ b/xen/include/asm-x86/hvm/vmx/vvmx.h
@@ -181,8 +181,8 @@ enum vvmcs_encoding_type {
 
 u64 get_vvmcs_virtual(void *vvmcs, u32 encoding);
 u64 get_vvmcs_real(const struct vcpu *, u32 encoding);
-void set_vvmcs_virtual(void *vvmcs, u32 encoding, u64 val);
-void set_vvmcs_real(const struct vcpu *, u32 encoding, u64 val);
+unsigned long set_vvmcs_virtual(void *vvmcs, u32 encoding, u64 val);
+unsigned long set_vvmcs_real(const struct vcpu *, u32 encoding, u64 val);
 
 #define get_vvmcs(vcpu, encoding) \
   (cpu_has_vmx_vmcs_shadowing ? \
-- 
2.7.4


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